1) It is important because the System helps an average person to locate herself precisely anywhere on the planet without having to be too much technically literate and for free.
2) It allows you to locate yourself on the high seas or featureless Saharan desert where there may not be any landmarks to orient yourself because it does not depend on any terrestrial system such as as its predesessor LORAN (because it is space based). Remeber, all printed maps require some kind of landmarks and routes on them for reference to be useful, still they do not 'show' your own location on them, a GPS receiver does.
3) Because it allows for rescue of fellow humans in situations such as natural disasters like earthquakes in a timely manner which was not possible before
4) Because it encourages the innate desire of humans to explore the unknown lands without the fear of not being able to return
5) Because it quietly helps protect our soldiers in times of conflict and in hostile lands by helping them navigate themselves and by helping others to find them if needed
6) These are some of more important reasons. However one could find many recreational and commercial reasons as well.